Irrigation systems that have been utilized in the past generally consisted of a number of spray orifices which discharge water in rather large area over a predetermined time. Recent developments have indicated that it is possible to irrigate with substantially less water than by spray irrigation or flood irrigation by applying water to crops in small quantities and utilizing subsurface irrigation where moisture moves into the soil through the hairline crack therein. When water is applied in small amounts, less water is lost in evaporation and runoff. The present system of applying water in small quantities is through the use of an orifice through which water may trickle from irrigation pipes that are laid out in the normal grid-like manner as disclosed in U.S. Pat. No. 3,547,355. When a small orifice is utilized, clogging of the orifice occurs due to particles that are entrained in the water system. Additionally, orifices are responsive to pressure in the line and the flow through each orifice has to be adjusted down the line so that the decrease in pressure as one gets near the end can be compensated for. This means in practice that each orifice has to be individually adjusted.